1. Field of the Invention
The present invention relates generally to the manufacture of semiconductor devices, and more particularly to a method for impregnating aluminum conductors or interconnections on such devices with copper to inhibit electromigration.
2. Description of the Prior Art
Aluminum conductors or interconnects formed on semiconductor devices suffer from electromigration caused by high current flow through the conductor. In the most severe cases, the electromigration can result in complete deterioration of the conductor and a break in the connection. Such electromigration can be lessened, however, by alloying the aluminum with a small amount of copper, typically from 0.5 to several weight percent. Heretofore, this aluminum-copper alloy has usually been deposited from single or dual evaporation sources, or by sputtering.
Unfortunately, the copper in the aluminum-copper alloys render the alloy resistant to chlorine plasma etching. The copper chlorides which are formed during the etching process inhibit further etching. Moreover, after the etching is completed, some copper chlorides will remain. Since copper chlorides are hydroscopic, they will absorb water when exposed to the atmosphere and form hydrochloric acid which will corrode the adjacent aluminum.
For these reasons, it would be desirable to provide a method for forming aluminum-copper interconnects, which method avoids the necessity of plasma etching aluminum-copper alloys and which does not leave residual copper chloride to corrode the aluminum.